infixapp.java

此代码主要功能是用堆栈来实现数学表达式的解析功能

package StackQueue;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class InfixApp {

	
	public static void main(String[] args) throws IOException {
		String input,output;
		while(true){
			System.out.print("Enter infix:");
			System.out.flush();
			input=getString();
			if(input.equals(""))
				break;
			IntoPost theTrans=new IntoPost(input);
			output=theTrans.doTrans();
			System.out.println("Postfix is"+output+'\n');
		}

	}
	public static String getString() throws IOException{
		InputStreamReader isr=new InputStreamReader(System.in);
		BufferedReader br=new BufferedReader(isr);
		String s=br.readLine();
		return s;

}
	}

// ///////////////////////////////////////////////////class InToPost
class IntoPost{
	private PublicStack theStack;
	private String input;
	private String output="";
	public IntoPost(String in){// 构造函数
		input=in;
		int stackSize=input.length();
		theStack=new PublicStack(stackSize);// 栈对象
	}
	public String doTrans(){
		for(int j=0;j<input.length();j++){
			char ch=input.charAt(j);
			switch(ch){
			case '+':
			case '-':
				gotOper(ch,1);
				break;
			case '*':
			case '/':
			    gotOper(ch,2);
			    break;
			case '(':
				theStack.push(ch);
				break;
			case ')':
				gotParen(ch);
				break;
				default:
					output=output+ch;
				break;
			}// end switch
		}// end for
		while(!theStack.isEmpty()){
			output=output+theStack.pop();
		}
		return output;
	}
	public void gotOper(char opThis,int prec1){
		while(!theStack.isEmpty()){
			char opTop=theStack.pop();
			if(opTop=='('){
				theStack.push(opTop);
				break;
			}
			else{
				int prec2;
				if(opTop=='+'||opTop=='-'){
					prec2=1;
					}
				else{
					prec2=2;
				}
				if(prec2<prec1){
					theStack.push(opTop);
					break;
				}
				else
					output=output+opTop;
			}// end else
		}// end while
		theStack.push(opThis);
	}// end gotOper
	
	public void gotParen(char ch){
		while(!theStack.isEmpty()){
			char chx=theStack.pop();
			if(chx=='(')
				break;
			else
				output=output+chx;
		}// end while
	}// end gotParen
	
}